1. Field of the Invention
This invention relates to an undervoltage release device for a circuit breaker. In particular, this invention relates to an undervoltage release device for a circuit breaker which is actuated by a trip coil. Still more particularly, this invention relates to an undervoltage release device for a circuit breaker which incorporates an electromagnetic device for sensing the undervoltage condition of a control voltage, and a chargeable trip spring for tripping the circuit breaker by means of the energy stored in the trip spring.
2. Description of the Prior Art
An undervoltage release device for a circuit breaker has the task of tripping the circuit breaker when the voltage under control or control voltage is reduced to a critical level. For this purpose, a circuit breaker is conventionally equipped with a normal trip coil.
In some presently known circuit breakers, electromagnetic sensing devices such as solenoids are used for sensing of the undervoltage condition of the control voltage. It is also known to trip a circuit breaker by means of energy stored in a charged spring.
In another presently known version of a circuit breaker, the undervoltage condition is sensed through a capacitor-relay system which energizes the trip coil of the circuit breaker. In such an approach, the aging of the capacitor has to be taken into consideration. The capacitor has only a definite life time, and therefore, the undervoltage release device of the circuit breaker has only a limited reliability. It is, however, an important objective in this technical field to design long-lasting tripping mechanisms for circuit breakers.
In some presently known circuit breakers, there may be a hazard that the circuit breaker is not tripped when the control voltage suddenly reduces to or below a critical value at which the normal trip coil of the circuit breaker does no longer activate. This means loss of control of the circuit breaker which is a great disadvantage especially as short circuit conditions.
It has to be understood, therefore, that the undervoltage release device should also perform a switching operation when the control voltage reduces to and below a critical voltage level at which the normal trip coil of the circuit breaker does not activate.